Light-emitting diodes (LEDs) are becoming more prominent as replacements for conventional incandescent light bulbs. Ideally, an LED bulb directly replaces a conventional incandescent light bulb. For example, a user simply unscrews the conventional incandescent light bulb and replaces it with an LED bulb. The LEDs within the LED bulbs operate on direct current (DC) whereas the incandescent light bulbs operate on alternating current (AC), which presents some obstacles with direct replacements of incandescent light bulbs with LED bulbs.
One of the obstacles in replacing LED bulbs with incandescent light bulbs is dimming. Conventional dimmers for incandescent light bulbs do not work with LEDs. In order to obtain a dimming function without replacing the conventional dimmers, the LED bulbs need to have a controller that senses the dimming and outputs a DC current to the LEDs that is proportional to the dimming. This conversion presents problems with the power factor in LED bulbs. Ideally, the input current and input voltage should be in phase to achieve a high power factor. In order to achieve a high power factor in LED applications, a power factor correction circuit is used to provide DC current to the LEDs and keep the input AC voltage and current in phase.
In an ideal power factor correction circuit, the correction method is such that the input current is made to match the input voltage very closely. That places certain demands on how the output current driving the LEDs is drawn. In a simple LED driver, it is desirable for cost reasons to implement the AC to DC conversion in a single step. This means the LED current must also follow the input line voltage to achieve a high power factor.
In non-dimming applications, the LED current may follow the input tine voltage. However, in dimming applications, this relationship causes issues with components used in the dimmers, such as triacs. For example, power factor correction circuits and methods may cause compatibility problems, which cause the user to see flicker in the light output by the LED bulb.